1. Field of the Invention
The present invention relates generally to electric power supplies, and more specifically to redundant, automatic switching power supplies. Even more specifically, the present invention relates to mutual isolation of inputs to redundant power supplies.
2. Discussion of the Related Art
For many critical or important electrical and/or electronic equipment or systems, it is desirable to have an alternate, or xe2x80x9cstandby,xe2x80x9d power source if a primary power source is lost or becomes unreliable.
A few examples of such equipment or systems are computer systems for hospital operating rooms and critical care equipment, air traffic control systems, police and fire emergency equipment, telecommunications systems, and national security systems. As may be imagined, the failure of a power supply to deliver a predictable power can have serious and potentially dangerous consequences.
It is, therefore, common to provide standby electrical power supplies to provide redundant power to a primary power supply. Commonly, the primary power is supplied by a local utility company at, e.g., 240 volts AC or 120 volts AC at 60 Hertz.
Many types of standby power sources are available, including turbines, micro-turbines, battery powered inverters rotary engines, internal combustion engines, and more recently, high-speed electrical generators and flywheels have been developed. These standby power sources may vary from the primary power in terms of voltage, phase and frequency. Thus, the primary and standby power supplies may be unsynchronized, and if the primary and secondary supplies are applied to a load simultaneously, potentially harmful voltage spikes and current surges may occur.
To prevent interaction between primary and standby power sources some redundant power supplies have elaborate break before make switching to assure that alternating current sources of different voltages and frequencies do not get connected together.
In other applications where a load operates from direct current, some redundant power supplies connect the primary and standby supply inputs with diodes after each input has been full wave rectified. This type of configuration, however, does not eliminate the possibility of voltage multiplication if, for example, the primary and standby sources are operating from different grounds.
The present invention advantageously addresses the needs above as well as other needs by providing switching means on the rectified outputs of power supply inputs to isolate the inputs from mutual electrical interaction.
In one embodiment, the invention can be characterized as a power supply comprising: a rectified output, a first rectified power supply including a first rectified supply switch wherein the first rectified power supply is detachably coupled to the rectified output with the first rectified supply switch, a second rectified power supply including a second rectified supply switch wherein the second rectified power supply is detachably coupled to the rectified output with the second rectified supply switch, a first rectified power supply inhibitor electrically coupled with the second rectified power supply and communicatively coupled with the first rectified supply switch, and a second rectified power supply inhibitor electrically coupled with the first rectified power supply and communicatively coupled with the second rectified supply switch.
In another embodiment, the invention can be characterized as a method of providing switching between alternative power supplies comprising the steps of: sensing a first rectified voltage of a first rectified power supply, sensing a second rectified voltage of a second power supply, maintaining a second rectified power supply inhibit signal and maintaining a closed first rectified power supply switch in response to the first rectified voltage of the first rectified power supply being at least a predetermined voltage level, maintaining an open second rectified power supply switch in response to the second rectified power supply inhibit signal, opening the first rectified power supply switch, removing the second rectified power supply inhibit signal, closing the open second rectified power supply switch and providing a first rectified power supply inhibit signal in response to the first rectified voltage of the first rectified power supply being less than a second predetermined voltage level and the second rectified voltage of a second power supply being at least a second predetermined voltage level, and maintaining the opened first rectified power supply switch in response to the first rectified power supply inhibit signal.
In a further embodiment, the invention may be characterized as a power supply comprising: a first power supply with a first rectified voltage, a second power supply with a second rectified voltage, an ultimate rectified output, a second power supply inhibiting means for providing a second power supply inhibit signal in response to the first rectified voltage being at least a first predetermined voltage and removing the second power supply inhibit signal in response to the first rectified voltage being less than the first predetermined voltage, a first power supply inhibiting means for providing a first power supply inhibit signal in response to the second rectified voltage being at least a second predetermined voltage and the first rectified voltage being less than the first predetermined voltage, a first switching means for disconnecting the first rectified voltage from the ultimate rectified output in response to the first rectified voltage being less than the first predetermined voltage, a second switching means for providing the second rectified voltage to the ultimate rectified output when the second rectified voltage is at least the second predetermined voltage and the second power supply inhibit signal has been removed.